Scientists at a hearing yesterday held by the House of Representatives Select Committee on Energy Independence and Global Warming tackled the question of regulating black carbon. Researchers know the particles, the main component of soot, warm the air and darken ice when they land on it, but the Environmental Protection Agency can't quantify the amount that the United States emits each year. Scientists estimate the pollutant was responsible for half the warming[2] in the Arctic since 1890, and could be warming the globe with more than half[3] the so-called "forcing" that carbon dioxide does.

As the science of soot has become clearer, Congress as well as international climate negotiators have begun to consider their options for reducing soot, but scientists testifying at the hearing said they should act faster.

As part of the 2009 stimulus package, EPA received and distributed $300 million [4] to convert diesel engines in municipal buses and other vehicles to cleaner burning designs-but received an additional billion dollars worth of project proposals. In the West, the main producers of soot are diesel engines, but the Clean Air Act gives EPA the authority to regulate only 9% of the 11 million diesel engines in use today. Conrad Schneider of the Boston-based Clean Air Task Force told the House committee that the Waxman-Markey bill, passed last summer by the House, directed EPA to clean up the 1 million engines it regulates through rules covering new vehicles or engine repairs. Schneider urged the lawmakers to tighten standards to cover all 11 million vehicles. That move would surely be controversial with makers and users of heavy machinery, but Chair Representative Ed Markey (D-MA) and Representative Jay Inslee (D-WA) seemed interested.

In developing nations, the main sources of soot are cook stoves and open fires in rural villages. Waxman Markey includes a program that would calls for U.S. aid to foreign nations to build cleaner burning stoves and set standards for them. But it doesn't provide money; Schneider suggested allocating revenues from any cap-and-trade scheme to do so.